A fluorescent lamp has been widely used from global environmental protection and economic standpoints because it has a higher degree of efficiency and a longer life as compared with an incandescent lamp. In recent years, as an economical light source, an electrodeless self-ballasted fluorescent lamp having no electrode has been attracting much attention since its life is several times longer than that of a conventional self-ballasted fluorescent lamp having electrodes, and the demand for an electrodeless self-ballasted fluorescent lamp is on the increase.
Furthermore, a self-ballasted fluorescent lamp in which a fluorescent lamp and a ballast circuit therefor are integrally formed is becoming a focus of attention as an energy-saving light source in houses, hotels, restaurants or the like, and is now becoming widespread because the self-ballasted fluorescent lamp can be readily used as it is in place of an incandescent lamp. In addition to the self-ballasted fluorescent lamp of this type having electrodes, the self-ballasted fluorescent lamp of this type having no electrode is also under development.
With the widespread use of the self-ballasted fluorescent lamp, as with a dimmable incandescent lamp, the need for dimming of the self-ballasted fluorescent lamp is being created. To be more specific, in houses or hotels, people carry out various daily living activities such as reading or spending a happy time with family, and in order to achieve a comfortable light environment adapted to these daily living activities, a user desires brightness suitable to each situation and seeks a function that realizes such brightness. Since an incandescent lamp does not emit light by discharge, it can be easily dimmed by merely adjusting electric power supplied thereto. On the other hand, since a fluorescent lamp emits light by discharge, it is difficult to implement a dimmable fluorescent lamp that can be practically used by merely adjusting electric power supplied thereto like an incandescent lamp.
Lately, in response to a need for a user to change brightness utilizing an already-known incandescent lamp dimmer as with an incandescent lamp, a self-ballasted fluorescent lamp with electrodes, which is connected to an incandescent lamp dimmer and allows dimmable operation, has been developed (see Japanese Unexamined Patent Publication No. 1999-111486, for example). However, the fact is that an electrodeless self-ballasted fluorescent lamp which is dimmable has not yet developed.
Besides, a self-ballasted fluorescent lamp having electrodes requires preheating of the electrodes for the discharge of electrons therefrom, and thus needs a voltage of a certain level. Therefore, if deeper dimming is carried out using a fluorescent lamp having electrodes, extinguishing occurs at the instant when a dimming voltage becomes lower than a voltage required for preheating of the electrodes, thus making it impossible to carry out smooth dimming.
The present applicant has already developed an electrodeless self-ballasted fluorescent lamp that is dimmable, and succeeded in completing such a lamp; however, this lamp still has inadequacies. For example, undesired extinguishing or flickering of the lamp occurs when low level dimming is carried out, and therefore, smooth dimming operation might not be achieved.
The present invention has been made in view of the above-described problems, and its main object is to provide an electrodeless self-ballasted fluorescent lamp and a discharge lamp operating device which achieve smooth dimming operation.